The present invention relates generally to vapor canisters for vehicles and, more particularly, to a volume compensator assembly for a vapor canister of an evaporative emission system in a vehicle.
It is known to provide a fuel tank in a vehicle to hold fuel to be used by an engine of the vehicle. It is also known to provide a vapor recovery and storage or evaporative emission system for the vehicle to reduce evaporative emissions of the fuel from the vehicle. Typically, the evaporate emission system includes a vapor canister remotely mounted such as in an engine compartment of the vehicle and operatively connected by separate external valves and lines to the fuel tank. However, the evaporative emission system is prone to permeation and bleed emission losses, has limited vapor storage capacity, and limited vapor flow rate acceptance.
New low emission vehicle requirements greatly reduce the amount of evaporative emissions allowed from the vehicle. The low levels now required effectively move the emissions from the xe2x80x9cbreakthroughxe2x80x9d levelxe2x80x94where the canister""s carbon capacity was fully utilizedxe2x80x94to the xe2x80x9cbleedxe2x80x9d level. These bleed emissions are hydrocarbon vapors that escape to atmosphere through migration of the canister""s hydrocarbon heel.
Current evaporative emissions canisters include volume compensation for the activated carbon contained within the canister. This compensation is necessary to provide an adequate carbon pack during the canister life expectancy. Without adequate pack, the carbon particles erode against each other or make flow paths for hydrocarbons to escape without being adsorbed. Erosion or open flow paths within the carbon bed lead to emission failures or vehicle diagnostic trouble codes. There are two main factors that contribute to the need for volume compensation of the carbon bed. First, over its life, the canister is exposed to vibration, impacts, and other motion that causes the carbon bed to endure some surface erosion and shifting of carbon particles to a tighter pack. Secondly, exposure to wide ranges of temperature cause the molded plastic canister body to expand and contract, adjusting the internal area where the carbon bed is contained. Adequate compensation allows the carbon bed to remain intact and capable of performing without deterioration.
Volume compensators have evolved along with canisters over the past twenty-five years. The first canisters, which were relatively small and molded with rigid plastic, did not incorporate volume compensators. As canisters began to increase in size and utilized a less rigid but higher impact resistant shell materials, volume compensation was needed. The initial volume compensators were an assembly of two molded trays having a plurality of openings therethrough that captured two springs. The volume compensator is typically the last component assembled into the canister prior to welding the bottom cover onto the canister and sealing the carbon bed inside. This design was adequate, but limited by high cost, many assembled pieces, and a large packaging space. The second generation of volume compensation changed to a stamped metal plate having a plurality of openings therethrough with an attached spring. The complexity, cost, and packaging issues were dramatically improved. The second generation volume compensator changed the internals of the canister and enhanced performance. Two distinct chambers were created internally, eliminating the ability to use a single volume compensator for the canister, thus requiring a volume compensator for each chamber of carbon. This chambering forced the flow of air through the canister (filling, purging) to travel through the volume compensator plates. The volume compensators had a plurality of openings therethrough for maximum flow area to prevent any increase in flow restriction through the canister.
With these volume compensators, as hydrocarbons from the fuel tank are vented to the vapor canister, they are adsorbed into the carbon bed and prevented from exiting to the environment. However, as the vapor canister is subjected to time and diurnal temperature variation, the hydrocarbons in the carbon bed begin to migrate towards the air-inlet tube of the vapor canister. The bleed emissions are not sufficiently captured as a result of these volume compensators, producing an unacceptable performance of the vapor canister.
Therefore, it is desirable to provide a volume compensator for a vapor canister for compensation of carbon volume. It is also desirable to provide a single-hole volume compensator to improve diurnal bleed emissions performance of a vapor canister. It is further desirable to provide a volume compensator in a vapor canister that minimizes flow restriction and is easier to package in a vapor canister.
It is, therefore, one object of the present invention to provide a new volume compensator for a vapor canister in a vehicle.
It is another object of the present invention to provide a single hole volume compensator for a vapor canister in a vehicle.
It is yet another object of the present invention to provide a volume compensator for a vapor canister that aids in the diurnal emissions performance of the vapor canister while minimizing flow restriction.
To achieve the foregoing objects, the present invention is a volume compensator assembly for a vapor canister including a partition adapted to be disposed in an interior chamber of the vapor canister and having a single opening extending therethrough. The volume compensator assembly also includes a grid pattern disposed on the partition about the opening to guide airflow to the opening. The volume compensator assembly further includes a spring connected to the partition and contacting the vapor canister to move the partition for compensation of a volume of a bed of vapor adsorbing material in the vapor canister.
One advantage of the present invention is that a volume compensator assembly is provided for volume compensation of a carbon bed in a vapor canister. Another advantage of the present invention is that the volume compensator assembly has a single opening that aids in the diurnal emissions performance of the canister by hindering the migration of the hydrocarbons in the carbon bed of the vapor canister. Yet another advantage of the present invention is that the volume compensator assembly has a single opening and grid pattern that provides a low flow restriction for the vapor canister that does not affect the fuel system during refueling and canister purging. Yet another advantage of the present invention is that the volume compensator assembly has a single opening and grid pattern that minimizes overall thickness of the volume compensator to package easily in the vapor canister without impacting overall vapor canister size. Still another advantage of the present invention is that the volume compensator assembly has a single opening and grid pattern that improves diurnal bleed emissions performance, minimizes flow restriction, and has a low profile for easy packaging and assembly. A further advantage of the present invention is that the volume compensator assembly has a single opening that does not impact cost.
Other objects, features, and advantages of the present invention will be readily appreciated, as the same becomes better understood, after reading the subsequent description taken in conjunction with the accompanying drawings.